This week: what you need to know about a inflammatory breast cancer, which is traditionally known as the one that can't be seen on a mammogram.

"Inflammatory breast cancer is a very fast growing kind of cancer because it actually means cancer cells are invading the lymphatics of the skin itself," said Dr. Julie Margenthaler with the Siteman Cancer Center.

When that happens, the breast becomes swollen, the skin red and warm. It can even take on the appearance of an orange peel. There is no tumor or lump.

"Inflammatory breast cancer has traditionally been known as the one that cannot be seen on mammogram and in some ways that's true however most women who have inflammatory breast cancer have an obvious abnormality," said Dr. Margenthaler.

But compared to other types of breast cancer, it's unusual. Only one to five percent of all breast cancers are inflammatory.

"It is a very serious form of breast cancer but it can be effectively treated with a combination of medication chemotherapy and surgery," said Dr. Margenthaler.

It can be an aggressive cancer, so if you notice any changes to the skin that don't clear up quickly, call your doctor.

"We would want to treat an infection if that's is what we think is going on and if it doesn't resolve, a biopsy can be done to determine if it's something more serious," said Dr. Margenthaler.